Thin film magnetic recording disks and disk drives are conventionally employed for storing large amounts of data in magnetizable form. Data are written onto and read from a rapidly rotating recording disk by means of a magnetic head transducer assembly that flies closely over the surface of the disk. The escalating requirements for high areal recording density and increasingly smaller disk drives impose increasingly demanding requirements on thin film magnetic recording media in terms of coercivity, remanence, coercivity squareness, low medium noise and narrow track recording performance. Considerable effort has been expended in recent years to produce magnetic recording media having high areal recording densities while satisfying such demanding requirements, particularly for longitudinal recording.
In order to realize ultra-high areal recording density, magnetic recording media with high coercivity and small Mrt (magnetic remanence.times.film thickness) are needed. E. Murdock, "Roadmap for 10 Gb/in.sup.2 Media: Challenges", IEEE Trans. Magn., Vol. 28, No. 5, pp. 3078-3083, Sep. 1992. Conventional magnetic recording media comprise a cobalt (Co)-based magnetic alloy layer, such as polycrystalline cobalt-chromium-tantalum (CoCrTa), cobalt-chromium-platinum (CoCrPt) or cobalt-chromium-tantalum-platinum (CoCrTaPt). A conventional magnetic recording medium structure is schematically depicted in FIG. 1 and comprises a non-magnetic substrate 10, typically a nickel-phosphorous (Ni--P) plated aluminum (Al) alloy, e.g., an aluminum-magnesium (Al--Mg) alloy, and sequentially formed thereon an underlayer 11, typically Cr or a Cr alloy, a magnetic alloy layer 12, typically a Co alloy, a protective overcoat 13, typically carbon or silicon dioxide, and a lubricant topcoat 14.
Cobalt-samarium (CoSm) magnetic alloy films are known to exhibit a high magnetic anisotropy constant and fine grain structures. U. Kullmann, E. Koester, and C. Dorsh, "Amorphous CoSm Thin Films: A New Material for High Density Longitudinal Recording", IEEE Trans. Magn., Vol. 20, No. 2, pp. 420-424, Mar. 1984. Accordingly, a CoSm magnetic alloy layer can be viewed as a potential candidate for high density longitudinal recording media. One such CoSm thin film containing magnetic recording medium has been attempted. E. M. T. Velu and D. N. Lambeth, "CoSm-based high-coercivity thin films for longitudinal recording", J. Appl. Phys. 69(8), pp. 5175-5177, Apr. 15, 1991. Such a potential CoSm thin film magnetic recording medium is schematically illustrated in FIG. 2 and comprises an alternate type non-magnetic substrate 20, such as a glass substrate, a Cr or Cr alloy underlayer 21, a CoSm magnetic alloy layer 22 and a protective carbon overcoat 23 thereon. Unfortunately, such a potential magnetic recording medium comprising a CoSm magnetic alloy layer exhibits low coercivity, e.g. about 2200-2300 Oersteads, and exhibits poor corrosion resistance.
There exists a need for a high areal density magnetic recording medium comprising a CoSm magnetic alloy layer which exhibits high coercivity and corrosion resistance.